The present invention relates to intraluminal grafts which are used for repairing defects in vessels and other lumens within the body. More particularly, the present invention relates to methods and systems for the endovascular repair of a defect using a flexible bifurcated modular graft.
Aneurysms are discrete dilations of the arterial wall. One of the most common, and among the most life threatening, is an aneurysm of the abdominal aorta between the renal and iliac arteries. If untreated, the aneurysm dilates progressively with an ever increasing risk of rupture and hemorrhagic death.
One method of treatment is provided by direct surgical intervention, in which the defective vessel may be bypassed or replaced using a prosthetic device such as a synthetic graft. The risks involved in direct surgical intervention of this magnitude are great, and include an extensive recovery period.
In recent years, a less invasive method of treatment has evolved through a series of inventions. The details vary, but, conventionally, a resilient tubular conduit fashioned from flexible fabric (herein referred to as a “graft”) is introduced into the defective vessel by means of catheters introduced into the femoral artery. The graft is attached to the non-dilated arteries above and below the aneurysm using expandable metallic cylinders (herein referred to as “support structures”).
Many abdominal aortic aneurysms extend to the aortic bifurcation, with the result that there may be no healthy vascular tissue at the lower end of the aorta, making it impractical to attach the lower end of the graft to the aortic wall. Accordingly, most cases of endovascular aneurysm repair employ a graft having a bifurcated shape, with a trunk portion and two limbs, each limb extending into an iliac artery where healthy tissue can be found for attaching the graft.
Bifurcated grafts may take one of two forms, depending on the method of insertion. Either the graft is inserted as a single element (unibody form), or it may be made up from more than one modular element which are assembled in vivo within the patient (modular form). Unibody grafts are positioned using a combination of catheters. In many of the current systems, orientation may be difficult to control, and twisting can occur. Moreover, the graft enters the patient having a fixed length based on preoperative sizing of the patient's vasculature. Thus, any error in preoperative sizing of the patient's vasculature may result in one or more orifice of the graft being incorrectly positioned.
Modular bifurcated grafts may overcome these difficulties. The insertion of a modular bifurcated graft conventionally commences with the insertion and positioning of a bifurcated trunk element of the graft within the aorta. Thereafter, up to two tubular limb elements may be inserted, being positioned to extend from orifices in the bottom of the trunk element to a certain distance within the iliac arteries. Each tubular limb is connected to the trunk element by means of a joint, which may be formed with the assistance of expandable support structures which are implanted at a point of overlap between trunk and limb elements and which, when expanded, form a pressure seal between the limb element and the trunk element. The staged insertion of the graft in modular elements as described above may reduce problems associated with orientation and twisting of the graft. It may also reduce problems associated with achieving the correct length of the graft, because it may be possible to customize the final length of the graft in vivo by varying the length of the overlap between the trunk and the limb elements. By using various size limb elements, the diameter of the flow path defined by the modular bifurcated graft also may be customized.
However, insertion of bifurcated grafts in modular form as described above may be attended by additional complications. The most troubling long-term complication is the disruption of a joint between the trunk and a limb element, which may be caused by vascular movement or forces generated by downstream fluid flow. Where the limb elements are individually added to the trunk element, there may be no mechanical restraint, other than the support structures, restraining the limb elements from downward movement. Thus, should the support structure holding the limb element in contact with the trunk element fail to operate as intended, due to excessive force or deformation of the support structure, extensive downward migration of the limb elements may result. Moreover, conventional methods used to form joints between elements of a modular bifurcated graft may result in an inadequate joint if insufficient overlap is provided between the elements, or if the elements are too rigid to accommodate unanticipated vasculature geometry.
Accordingly, there exists a need for an improved modular bifurcated graft that embodies robust junctions between modular elements thereof as well as structure which can accommodate a wide range of geometries. This invention addresses these and other needs.